The present technique used to warn a succession of motorists that one of them is slowing down or stopping, consists in providing vehicles with stop lights, the lighting of which is subject to the actuation of the brake pedal. When a vehicle is braked, its stop lights come on but only the immediately following driver can perceive this signal. The third driver in line does not begin to brake until the stop lights of the second vehicle come on, and so on. This results in cumulative information delays which may end up in a multiple pileup if one of the drivers is distracted or slow to react, if he is travelling too close to the preceding vehicle or if the visibility conditions are poor. The phenomenon is accentuated by the disparity in braking performance from one vehicle to another and in their respective loading.